Short cervix during pregnancy may contribute to preterm birth

Short cervical length in mid- to late pregnancy appears to increase the risk of preterm birth, according to a recent Singapore study.

“The aim of our study was … to determine the rate of spontaneous preterm birth and to analyse the distribution of cervical length and the relationship between preterm birth and cervical length in the pregnant Asian population here in Singapore,” researchers said. The findings may help identify at-risk patients for stricter monitoring and potential interventions.

The prospective observational study included 926 women with single viable pregnancies. Sixty-two (6.7 percent) mothers delivered prematurely, more than half of which were spontaneous; the others were triggered by iatrogenic interventions. [PLoS One 2020;15:e0230125]

At the first gynaecology visit, at 14 weeks of gestation, median cervical length was comparable between women who delivered at term and those who had spontaneous preterm births (3.10±0.64 vs 3.05±0.50 cm; p=0.425).

However, by the second (18–22 weeks; 3.20±0.71 vs 3.03±1.34 cm; p=0.028) and third (28–32 weeks; 3.10±0.71 vs 2.43±0.88 cm; p<0.001) visits, the researchers found that cervical length was significantly shorter in women who eventually delivered prematurely. By the final visit, after 34 weeks of gestation, the difference remained but was of only marginal significance (2.74±0.82 vs 2.21±0.73 cm; p=0.072).

Receiver operating characteristic curve analysis further highlighted the importance of cervical length for assessing risk. Shorter lengths at 18–22 weeks of gestation was decently predictive of preterm birth <37 weeks, with an area under the curve of 0.61.

Subsequent refinement revealed an optimal cut-off of 2.48 cm. At this value, the sensitivity and positive predictive values (PPV) were low, at 29.0 percent and 12.0 percent, respectively, but the specificity and negative predictive (NPV) values were high, at 90.1 percent and 96.5 percent, respectively.

Cervical length at 28–32 weeks was a more powerful predictor, with an area under the curve of 0.73. At the optimal cut-off of 2.49 cm, sensitivity was 54.8 percent, specificity was 82.5 percent, PPV was 11.1 percent, and NPV was 97.9 percent.

“Preterm birth is a condition that varies widely between different countries or ethnicities,” as does cervical length, the researchers said. “It may therefore be useful to generate nomograms for cervical length for each of the various ethnicities specific to a geographic location in view of these inherent differences between continents.”

“Also, more research needs to be conducted with regard to why this variation exists, so as to potentially find interventions that target the underlying contributors to this finding to reduce the rate of preterm birth,” they added.

In the present study, participants were enrolled from the KK Women’s and Children’s Hospital in Singapore. Those with multiple gestation and pre-existing autoimmune or renal diseases were excluded. Cervical length was measured using ultrasound at each of the four antenatal visits.